This invention relates to a flow control valve unit and more particularly to a valve unit for controlling a fluid flow through a fluid passage in which the motor rotation is converted into a translational movement of a valve.
FIG. 1 illustrates in section a structure of a previously proposed flow control valve unit 1 for controlling a fluid flow flowing through a fluid passage 2 defined in a block member 3 to which the valve unit is mounted. The valve unit 1 comprises a motor 4 having a rotary shaft 5, and a valve assembly 6 having a substantially tubular valve holder 7 axially movably mounted to an extension of the motor shaft 5, a valve member 8 securely attached to the valve holder 7 by a thread therebetween and a splined mold member 9 insert-molded with the valve holder 7 so that they are integrally connected.
The flow control valve unit 1 also comprises a conversion mechanism disposed between the motor shaft 5 and the valve assembly 6 for converting a rotational movement of the motor shaft 5 into an axial translational movement of the valve assembly 6. The conversion mechanism includes spiral splines 11 formed on the extension of the motor shaft 5 and spiral splines 12 formed in an inner surface of the mold member 9 and engaged with the splines 11 on the motor shaft 5. The conversion mechanism also includes an axially extending stationary guide 13 disposed on a tubular member 14 attached to the motor 4 and a guide groove 15 formed in the mold member 9 of the valve assembly 6 for an axially slidable engagement with the stationary guide 13. A compression spring 16 is disposed between the valve holder 7 of the valve assembly 6 and the tubular member 14 for eliminating play between the spiral splines 11 and 12. The compression spring 16 is surrounded by a metallic tubular member 17 attached to the valve holder 7 of the valve assembly 6.
The valve assembly 6 is coaxially supported on the motor shaft 5 by a guide metal 18 disposed between the valve holder 7 and the extension of the motor shaft 5. In order to limit an axial movement of the valve assembly 6 within a suitable range, a first stopper 19 is disposed on the motor shaft 5 between the motor 4 and the valve assembly 6 and a second stopper 20 is mounted on a front end portion of the motor shaft 5.
When the motor 4 is energized in an open position illustrated in FIG. 1 in which the valve assembly 6 is separated from the valve seat 2a of the fluid passage 2, the motor shaft 5 rotates to drive the valve assembly 6 to move forward along the shaft 5 due to the conversion mechanism including the spiral splines 11 and 12 and the axial guide 13. When the valve member 8 of the valve assembly 6 engages the valve seat 2a of the fluid passage 2, the valve assembly 6 is in a closed position in which the fluid passage 2 is closed by the valve member 8. The flow rate of the fluid flowing through the fluid passage 2 can be adjusted to any desired point between 0% and 100% according to the rotation of the motor. The forward movement of the valve assembly 6 is limited by the second stopper 20 which abuts against the shoulder portion of the valve holder 7, and the rearward movement of the valve assembly 6 is limited by the first stopper 19 which engages the rear end of the mold member 9 of the assembly 6.
In the above-described flow control valve unit, the valve assembly 6 comprises a number of components. That is, the valve assembly 6 comprises the metallic valve holder 7 machined to the desired configuration, the mold member 9 having the internal thread or spline 12 to which the metallic valve holder 7 is insert-molded, and the metallic valve member 8 formed by machining and secured to the valve holder 7 through threads, so that the number of parts is large and the assembly of these parts by the insert-molding and the thread fastener is time-consuming and inaccurate. More particularly, since valve holder 7 is insert-molded into the splined mold member 9, the precise axial alignment of the valve holder 7 relative to the internal spline of the mold member 9 cannot be obtained. Also, since the valve holder 7 and the valve member 8 are made by machining, the deviation in the dimensions of the assembled valve holder 7 and the valve member 8 is large. Therefore, during the assembly of these components, the dimensional deviations of the manufacturing tolerance of each component may be accumulated, providing only poor positional accuracy between the valve member 8 and the valve seat 2a of the fluid conduit 2. While an arrangement is proposed in which an adjusting mechanism for adjusting the positional relationship between the valve holder 7 and the valve member 8 is disposed between the valve holder 7 and the valve member 8, this arrangement results in a further increase of the number of parts, a complicated structure, difficulty in manufacture and in a high cost.